Proceedings of the Physiological Society, 13–14 April 1973, University of Southampton Meeting: Communications

Abstract

3TUAll current techniques for the estimation of renin in plasma are indirect methods relying on measurement of angiotensin produced during incubation with renin substrate. These methods assess the enzymic activity of renin rather than the actual rate of renin secretion by the kidney because of the possible involvement of renin inhibitors or activators. We have recently developed a new renin assay based on the rocket immunoelectrophoresis technique of Laurell (1966). This measures renin concentration directly, and has been used in dogs to investigate the relationship between the amount of renin in plasma and its enzymic activity before and after partial occlusion of one renal artery. The contralateral artery was ligated.Ten mongrel dogs were used. After completion of the preparative procedures a 2 hr period was allowed for equilibration. At intervals during the succeeding two hours three plasma samples were collected from the renal vein for estimation of renin activity using ovine substrate (Skinner, 1967) and renin concentration using the new assay procedure. Renal blood flow was monitored with an electromagnetic flowmeter. In six of the dogs a constriction which reduced flow to 30-40 % of normal was then applied to the renal artery. Three further samples were collected during the ensuing 2 hr period. A similar protocol with no renal artery constriction was used in the four control dogs. A theoretical renin activity based on the renin concentration assays was calculated using the renin activity of the standard renin. The ratio, theoretical to actual activity, served as an assessment of the efficiency of angiotensin II production in the plasma.The pooled data from all the dogs show an increase in mean plasma renin activity from 8-05 renin units (s.x. 0.97) to 46-2 renin units (s.x. 9.0) 70 P PHYSIOLOGICAL SOCIETY, APRIL 1973 following renal artery constriction (P < 0.001). The corresponding renin concentration estimations were 0-27 units (S.E. 0 03) and 0-35 units (s.E. 0.03), and the difference was not significant. An alternative way of expressing these results is that the ratio of theoretical to actual renin activity fell from 91: 1 before to 22: 1 after renal artery occlusion. In the control animals over the same time course there were no significant changes in either renin activity or concentration.These data indicate that the well documented increase in plasma renin activity following partial renal artery occlusion is not due to increased renin secretion from the kidney but rather to change in its enzymic activity. A conceivable explanation could be based on changes in the availability of renin inhibitor (Smeby, Sen & Bumpus, 1967) but we have no direct evidence to support this against other possibilities. In the light of these observations the theories covering control of renin release should be regarded as relating to the control of plasma renin activity, and many of these situations need reinvestigation with this direct renin assay method. The mechanism by which angiotensin causes retention of sodium in...